Query the views v$database and v$thread.
V$DATABASE gives DB_NAME
V$THREAD gives ORACLE_SID
If ORACLE_SID = DB_SID and db_name = DBNAME:
To find the current value of ORACLE_SID:
SVRMGR> select instance from v$thread;
INSTANCE
----------------
DB_SID
To find the current value of DB_NAME:
SVRMGR> select name from v$database;
NAME
---------
DBNAME
